Wall-rue: The Tiny Fern That Thrives Where Others Fear to Grow
If you’ve ever wondered what that delicate little fern growing out of an old stone wall might be, chances are you’ve spotted wall-rue (Asplenium rutamuraria). This charming perennial fern has earned its common name through its remarkable ability to make itself at home in the most unlikely places – particularly in the cracks and crevices of limestone walls and rocky outcrops.
A Native Gem with a Wide Range
Wall-rue is a true North American native, calling both Canada and the lower 48 states home. You can find this adaptable little fern growing naturally across a surprisingly wide range, from the Maritime provinces of New Brunswick and Quebec down through Ontario, and extending south through numerous states including Alabama, Arkansas, Connecticut, Georgia, Illinois, Indiana, Kentucky, Maryland, Massachusetts, Michigan, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, Tennessee, Vermont, Virginia, and West Virginia.
Important Conservation Considerations
Before you get too excited about adding wall-rue to your garden, there’s something important you should know: this little fern is quite rare in many areas. In Alabama, it carries a rarity status of S2 (imperiled), while in Arkansas it’s even rarer with an S1 (critically imperiled) designation. This means that if you’re lucky enough to encounter wall-rue in the wild, you should admire it from a distance and never attempt to collect it.
If you’re determined to grow wall-rue, only obtain plants from reputable nurseries that specialize in native plants and can guarantee their stock is responsibly sourced through propagation rather than wild collection.
What Makes Wall-rue Special
Wall-rue is quite the little character in the fern world. Unlike the large, showy ferns you might be familiar with, this diminutive species typically grows only 2-6 inches tall. Its fronds are uniquely divided into small, rounded segments that bear a striking resemblance to the leaves of the herb rue – hence its common name.
The fronds emerge from short, dark stems and have a distinctive blue-green to gray-green color that helps them blend seamlessly with their preferred limestone habitats. This coloration isn’t just for show – it’s an adaptation that helps the plant survive in its harsh, sun-exposed rocky environments.
Growing Conditions: Not Your Average Fern
If you’re thinking wall-rue might be happy in the same moist, shaded spot where your other ferns thrive, think again! This little rebel breaks all the typical fern rules:
- Prefers alkaline soil conditions (unlike most ferns that prefer acidic soil)
- Thrives in well-drained, even dry conditions
- Tolerates more sun exposure than typical woodland ferns
- Absolutely requires excellent drainage – wet feet will kill it quickly
- Grows best when planted directly into limestone rock crevices or very gritty, alkaline soil
Wall-rue is hardy in USDA zones 3-8, making it suitable for most temperate North American gardens, provided you can meet its unique cultural requirements.
Perfect for Rock Gardens and Alpine Settings
Given its specialized needs, wall-rue isn’t a plant for every garden situation. It’s absolutely perfect for:
- Rock gardens with limestone or other alkaline stones
- Alpine and scree gardens
- Stone retaining walls (especially those made with limestone)
- Crevice gardens
- Dry shade areas with alkaline soil
In these specialized settings, wall-rue can be a real showstopper, adding delicate texture and unique character to areas where few other plants can survive.
Wildlife and Ecological Benefits
While wall-rue doesn’t produce flowers to attract pollinators (being a fern, it reproduces via spores), it does play important ecological roles. Its ability to colonize bare rock faces helps begin the slow process of soil formation, and it provides habitat for small invertebrates that shelter among its fronds.
Care and Maintenance
Once established in suitable conditions, wall-rue is remarkably low-maintenance. In fact, the best care you can give it is benign neglect:
- Avoid fertilizing – it’s adapted to nutrient-poor conditions
- Don’t water unless experiencing extreme drought
- Never mulch around the plants
- Remove any competing vegetation that might crowd it out
- Protect from foot traffic, as the small size makes it vulnerable to being stepped on
The Bottom Line
Wall-rue is definitely not a plant for every gardener or every garden situation. Its rarity means it should only be grown from responsibly sourced plants, and its specialized growing requirements mean success isn’t guaranteed. However, if you have the right conditions – particularly a limestone rock garden or crevice garden – and can source plants ethically, wall-rue can be a fascinating addition that showcases the incredible diversity and adaptability of our native flora.
This little fern reminds us that sometimes the most interesting plants are the ones that dare to be different, thriving in places where others simply can’t survive.
